Emission gas recycling equipment according to a related art is well-known. In the equipment, an emission gas recycling gas (i.e., EGR gas) as a part of the emission gas flowing through an exhaust pipe of an engine is mixed into an intake air flowing through an intake pipe so that the maximum combustion temperature is reduced. Thus, toxic substance (e.g., a nitrogen oxide) included in the emission gas is reduced. However, when the emission gas is recycled, engine power is reduced, and driving performance of the engine is reduced. Therefore, it is required to control an amount of the recycling emission gas (i.e., an EGR amount), which is recycled into the intake pipe.
In the related art, the equipment includes a recycling emission gas amount control valve for adjusting an opening area of an emission gas recycling passage, which is formed in an emission gas recycling pipe of the emission gas recycling equipment. Here, emission gas recycling equipment using a butterfly valve as a valve body of a recycling emission gas amount control valve is disclosed in, for example, Japanese Unexamined Patent Publication No. H11-502582, which corresponds to U.S. Pat. No. 5,531,205. In this case, the butterfly valve is operated in a rotation direction by a torque motor through a valve shaft. Further, electric control type throttle control equipment using a butterfly valve as a valve body of an airflow amount control valve is disclosed in Japanese Patent Application Publication No. H04-249678, which corresponds to U.S. Pat. No. 5,146,887. In this case, the butterfly valve adjusts an opening area of an inlet passage disposed in an intake pipe connecting to a cylinder of an engine. Thus, the butterfly valve is stopped at a position, at which the valve is rotated by a predetermined angle in a case where the engine is stopped, so that the valve body is prevented from adhering to a bore by a deposit.
In the above prior arts, the butterfly valve rotates around a rotation center axis as a center of the valve shaft. The butterfly valve as the recycling emission gas amount control valve is accommodated in an emission gas recycling passage, in which an emission gas recycling gas (i.e., EGR gas) flows. The EGR gas includes a fine particle such as combustion residual or carbon. Therefore, when the butterfly valve is stopped at the valve full close position in a case where the engine stops, the fine particle in the emission gas recycling gas (i.e., EGR gas) may be adhered to the butterfly valve so that the deposition of the fine particle is occurred. If the deposit of the fine particle is deposited to bridge between the inner diameter surface of the passage and the outer diameter periphery of the butterfly valve, the butterfly valve is not operated smoothly by an actuator such as the torque motor.
In the above case, even if the butterfly valve is operated by energizing the actuator such as the torque motor, for example, in a case where the engine starts, the butterfly valve can not be returned to the valve full close position. Accordingly, the butterfly valve is not operated smoothly by the actuator such as the torque motor after the engine starts. Thus, a possibility of a problem exists, the problem being that the recycling emission gas amount (i.e., EGR amount) cannot be adjusted to correspond to the driving condition of the engine.
Further, another emission gas recycling equipment using a butterfly valve as a valve body of a recycling emission gas amount control valve is disclosed in Japanese Patent Application Publication No. 2003-314377. In this equipment, the butterfly valve has no seal ring, which seals a clearance between the inner diameter surface of a nozzle and an outer diameter surface of the butterfly valve when the butterfly valve is positioned at a valve full close position. Therefore, the butterfly valve is not adhered to an emission gas recycling passage. However, the recycling emission gas amount cannot be precisely adjusted to correspond to the driving condition of the engine, since the butterfly valve is not sealed.